Posted
by
samzenpus
on Thursday September 20, 2012 @11:33PM
from the a-bit-of-a-problem dept.

SchrodingerZ writes "The nuclear power station on Three Mile Island in Pennsylvania shut down abruptly this afternoon. Its shutdown was caused when one of four coolant pumps for a reactor failed to work. 'The Unit 1 reactor shut off automatically about 2:20 p.m., the plant's owner, Exelon Corporation, reported. There is no danger to the public, but the release of steam in the process created "a loud noise heard by nearby residents," the company said.' If radiation was released into the environment, it is so low that it thus far has not been detected. The plant is a 825-megawatt pressurized water reactor, supplying power to around 800,000 homes, thought there has been no loss of electrical service. Three Mile Island was the site of a partial nuclear meltdown in 1979. The Unit 2 reactor has not been reactivated since."

I'll reserve judgement on what's actually happened, because this industry has a history of salamitaktic, lying, cover-ups and manipulation of public opinion.

It's possible this innocuous announcement is the start of a series of press-releases, each admitting to progressively worse problems. If that's the case, all the Pollyannas on Slashdot will have vanished by the time the real scope of the event is clear.

Oh for fucks sake. There are event classifications if shit goes really wrong. Since they didn't even declare an Unusual Event (lowest of four classifications), things are under control. It appears that there may have been complications during the trip, but there is no emergency. And for your information, if there is an emergency the plant has to declare it within 15 minutes and inform state and local authorities within another 15 minutes. The people who make these decisions are licensed by the NRC and can be held personally responsible. They are also legally protected from any type of retaliation for taking action based on safety concerns. They aren't going to cover it up for three reasons: 1) their families live nearby, 2) the legal ramifications are severe, and 3) they could easily get another job at any other plant in the country (~2000 workers of their level of training in an industry that wants 3000 or 4000).

"Three Mile Island is still shutdown Thursday night. Around 220 Thursday afternoon, people who live near the nuclear power plant heard a loud noise, saw steam and then the plant automatically shut down.

"The Nuclear Regulatory Commission said Thursday that it was satisfied with Exelon’s repairs following a reactor shut-down at Three Mile Island on Aug. 22.

The NRC said a small leak in the reactor coolant system was caused by “micro-cracks” in a diaphragm in a pressurized heater bundle within the containment barrier. The cracked diaphragm was made of alloy 600; it was replaced with one made of stainless steel, and the unit was powered back up."

Oh for fucks sake. There are event classifications if shit goes really wrong. Since they didn't even declare an Unusual Event (lowest of four classifications), things are under control. It appears that there may have been complications during the trip, but there is no emergency.

IF something actually goes bad in Nuclear energy its very hard to cover up something that anyone can measure with a freaking tool!!!!
Stop spreading FUD, there's no high levels of radiation and that can easily be measured by anyone.
Wanna see cover ups in energy? Go look for carbon mines and fuel refineries and then tell me something. With far more accidents deaths and nature crimes per year each than all nuclear accidents combined.

ozmanjursi didn't post any fact and yes I dispute their claims. The nuclear industry in the US has proven to be safe, they promptly report even minor incidents, and to the best of my knowledge have never lied about conditions at their plants or the scope of an event. What happened in other countries has no bearing on what happens in the US until there is evidence to the contrary.

As osmifra points out, the fossil fuel power supply industry (mining up through the power plants themselves) do have a long history of raping the natural resources, not providing safe working conditions for their workers (miners), being horrible polluters, and having massive lobbying arms to make sure that any regulations that do get passed to curb these things have no teeth to actually stop them. Nuclear power, on the other hand, is very tightly regulated (see lobbying power of the fossil power as a big part of that) and does none of those things.

To be fair to the shitstorm, there are historical reasons to be a bit worried when Exelon describe something as a planned release of steam with minimal release of radioactive material. Lets hold out for the NRC report.

It doesn't sound like a graceful shutdown. We'll have to wait for the NRC event report tomorrow. A reactor cooling pump trip would typically initiate a reactor protection trip (scram). The steam generators would cool the primary by sending steam to the condenser steam dumps. Instead there was a loud noise which indicates that steam was being vented to the atmosphere via the atmospheric steam dumps. This implies that the main steam stops (isolation valves to the turbines) shut. Potential causes for that would be excessive cooldown (an interlock), loss of the condenser vacuum, or a secondary equipment fault. None of these is normal.

I'm guessing that it was probably an electrical fault. A reactor cooling pump trip and secondary pumps could be powered from the same electrical buses since they are not considered safeguards equipment. The other possibility is that the operators didn't control the cooldown properly, or there was an I&C fault that tripped an interlock for the main steam isolation valves.

Disclaimer: I'm familiar with Westinghouse PWRs, but not the Babcock & Wilcox PWRs. So take what I say with a grain of salt.

Of course it's not graceful but a shutdown as a result of equipment failure never is. Steam venting isn't graceful, but then neither is a SCRAM.

I work in the process industry and the only time a shutdown is ever graceful is through carefully planned and usually long duration operator actions. Even then some processes they just get it down to a stage where there will be minimal damage and then hit the trip button and hope nothing breaks.

The key thing here is what shutdown the process was a safety system which prevented a hazardous event from occurring, rather than hazardous event occurring and causing the shutdown. Compared to that this event really can be considered quite graceful.

Actually there is another rather important issue that has not been mentioned yet: reliability. TFA claims that the reactor which was forced to shut down was supplying 825MW. That means there had to be a spare 825MW capacity available instantly in the system to avoid a temporary black-out. Not just "we can spool this up in half an hour", but 825MW of on-line generation capacity being mostly wasted just to cover this eventuality.

As the system transitions away from centralized large scale generators to more di

As the system transitions away from centralized large scale generators to more distributed small scale electricity sources it becomes more efficient and more reliable.

True in some ways... Except when you are using standard "green" energy sources for power generation. Bad things happen when the wind stops blowing or a cloud drifts by. Even on the best day, you can only count on about 20% availability of capacity from wind or solar, which means you have 80% reserve capacity available from fossil fuels not being used. One green exception to this is hydro-electric, which can usually be throttled up in a very short time and doesn't usually suffer unplanned outages.

I don't think tidal would be useful at all times, but that aside... We've pretty much maxed out the hydroelectric capacity we have here in the US (unless you count the dams they are taking down) and geothermal capacity is *extremely* limited. Other "renewable" sources are not reliable enough to depend on for peak capacity needs.

Nuclear power is not a good source of peak capacity because they are hard (and/or expensive) to throttle up and down due to fuel cycle considerations. Fossil fueled plants will be

I don't think the plant had the spare capacity, but rather the grid did. 825MW is nothing compared to the difference between peak and base load for a large city. I'm not sure if America publishes openly the daily electricity trading stats like in my country but in my state which has a population less than 1/3rd that of Pennsylvania the peak to base swing changes by more than 5GW daily.

If you run your powerplants like we do with very little peak smoothing capacity then yes 825MW suddenly missing from the gri

It's called spinning reserve. Mostly turbines running at idle and hydro units that are river flow limited on generation anyhow. The hydro units in particular are not wasting any energy waiting to be called on. That said they are limited on ramp rate as putting a 'wall of water' down most rivers is not allowed (for good reasons; dangerous, erosive. Also strands fish when it stops). The exception there is when one reservoir cascades directly into another, those can more or less ramp as fast as the equipment will allow (which is pretty fast).

Also note: the system just lets the voltage drop (browns out) while the 'ready reserve' units spin up. 120 VAC is purely nominal. Talk to someone that designs 120VAC power supplies. They should function down to about 95V IIRC. This is by design.

Also also note: most transmission areas are both importing and exporting at any given time. They can always just cut their exports and shift a part of the issue to their neighbors. Increasing imports isn't likely to happen in the middle of the day. The lines were likely running at max capacity to begin with.

Voltage dropping was helpful when a lot of the load was resistive (incandescent lightbulbs, linear regulators in most low-voltage equipment, etc.). As the voltage dropped, the power demand dropped as well. These days, the switching power supplies are negative resistances and as the voltage drops the power demand doesn't drop. In fact, due to typically lower efficiencies with lower input voltage, the power demand goes up as the input voltage drops! From what I imagine, one fine day the U.S. grid won't be abl

A "graceful" emergency shutdown of a large thermal power station unit is actually bloody noisy as the steam goes into the blow down vessel/s.Also any water that touches the turbines doesn't actually go into the reactor, it goes through heat exchangers where the working fluid of the reactor is on the other side.Disclaimer: I'm familiar with the turbine side (fairly universal amoong all thermal power stations of the same size) but in my case the boilers were all coal fired. There are many similarities to the point where one of my co-workers was a Russian turbine engineer with a lot of nuke experience (and some scary stories).

This is a very accurate reply with one exception. Generally, the condenser can't support the steam output of the steam generators (they're normally rated around 10-25% of full load). Most plants in the US will steam dump to atmosphere because it's easier and doesn't put unnecessary strain on the equipment.

Plus, dumping to atmosphere has the added benefit is that the whole plant staff knows immediately that they are staying late.

Source: I am an I&C engineer that has worked on many US and European units.

I'm guessing that it was probably an electrical fault. A reactor cooling pump trip and secondary pumps could be powered from the same electrical buses since they are not considered safeguards equipment

I don't know why this is modded down - its absolutely correct. Nuclear reactors are designed to be "fail safe". If a pump breaks, the system shuts down. There are probably backup pumps in case the shutdown fails too, etc.

Pressurized Water Reactors (PWR) are designed to fail safe using active intervention mechanisms and totally don't fail safe if the active mechanism screws up as it did in Fukushima. Personally I would dig up the long dead generals of the nuclear weapon testing era and Kill Them all again for the crime against humanity that they committed. What crime you ask? The crime of denying the world cheap and safe nuclear power.

All of the modern worlds reactors are fundamentally unsafe PWR reactors which were designed

That's not what fail safe means. In this case when the pump failed a number of things had to happen for the failure to be safe. The reactor probably SCRAMed and emergency cooling kicked in. Without those systems and careful management by staff the reactor could fail like Fukushima did.

If it were fail safe the failure of the pump itself would have made the whole thing completely shut down into a safe and inactive state. I used to work in fire suppression for buildings and when we had a fire door that was "fail safe" that meant it was held locked shut by an electro magnet, so if the power failed for some reason it would automatically unlock and allow people to escape. In fact even if the control system stopped communicating it would open. No action by anyone or anything else required.

This thinking shows that you have absolutely no clue about how real functional process safety engineering is done. Fail safe means that when you have a certain number of failures (for a nuke plant probably two), things are still safe. So you can have, say, a concurrent turbine trip and a pump failure in a primary circuit, and things should end up in a safe state. Fail safe doesn't imply passive safety, it's only your fantasy and a view that's not shared by those who actually deal with functional safety. Pas

From the 1960s and 1970s, ~40 years, but dont worry they many in the US got a rubber stamp extension:)
20-year extensions where granted, so expect to see 80 years, and then 100.
The designed for a duty cycle is now a historical number, a better understanding of earthquakes and flooding is put to one side.
The sub systems are also an interesting risk, you can have a great reactor, lots of diesel ready, good protected diesel generators, extra staff on site after they all get called back in - if the cooling

As far as I'm aware (and that's not that far, but far enough to reply to this) this kind of pressurized water reactor cannot really shutdown very gracefully. Once such a reactor gets going at normal power levels for some time, it can not shutdown very quickly. The best it can do, is to stop most of the fission reaction (in this case probably a so called Emergency SCRAM). Afterward the SCRAM, the fuel rods will still be Pretty Hot and initially they will still produce about 7% of their normal power due to fission product decay. After a day that's down to about 0.4%, which in this case would still be something like 4 megawatts or so. More than enough to keep things in a closed, well-isolated reactor Really Hot for months to come.

So, in fact, the shutdown-sequence is not graceful at all; it is an extended process that requires active cooling (and therefore working power) and supervision and will result in disaster if it is interrupted for some amount of time.

Yes, if this was a coal or natural gas plant such an issue wouldn't even make the news. But it is a Scary Nuclear Power plant then it must mean there is a HUGE Poroblem even though the fail safes all worked correctly. Because Nuclear is Scary.

I am not saying Nuclear is Clean, Safe to Cheap to Meter. But really it is one of our better power sources, and we should be sure that we support nuclear and support proper regulation on this energy source as it has a lot of long term dangerous elements to it.

I am not saying Nuclear is Clean, Safe to Cheap to Meter. But really it is one of our better power sources, and we should be sure that we support nuclear and support proper regulation on this energy source as it has a lot of long term dangerous elements to it.

This incident just illustrates the point that nuclear isn't well regulated enough and probably never will be. TMI is an old design that should be been shut down a long time ago and replaced. That would cost a lot of money though so instead the license just keeps getting extended.

At this point someone will usually suggest thorium as the solution to all our problems, but the economic reality of building such a plant makes it impossible. No-one is willing to pay the cost, not investors, companies, the governme

But, to be fair, isn't this how these things are suppose to work? Something fails, everything gracefully shuts down?

Which won't stop every envirowhack on slashdot from waving his hankie and screaming "NUKLYUR EVIL!!".

It's not nuclear power that is evil, it's the fuckwads who end up working there and/or in charge of it. My father used to work in nuclear power stations, and he said once that the opening credits of The Simpsons are closer to reality than most people would like to think.

I'm sorry, but with the nuclear power industry, it's always jam tomorrow. It needs to be tightly controlled by people with no vested financial interest in it, but of course that is too fucking socialist for everyone nowadays.

And here we see a member of the "NUKLYUR EVIL!!" crowd in action. Unconfirmable anecdote combined with unrealistic solutions. Bonus points for whining that someone thinks solution will be too "socialist".

"Basically, when you add the costs of decomissioning and waste storage, they become pretty expensive. For the tax payer, of course."

Actually no. US and most other Western power reactor operators pay into funds for decommissioning their reactors and also for waste disposal on a kWhr basis. The US rate for waste disposal is 0.25 cents/kWhr which goes to the US government as it is in charge of all high-level nuclear waste since it is seen as a security risk. The current fund total is about 36 billion dollars IIRC. It's the taxpayer that has to deal with coal-slurry lagoons, mercury and other nasties in the exhaust stack, the buildup of CO2 in the atmosphere etc. Legislative attempts to cut down such releases under the EPA and such are a "war on coal" according to, surprise suprise, the coal-mining and coal-burning industry.

As for nuclear power costs in the US, fuel costs are about 0.5 cents/kWhr and operations (running the plant, refurbishing the generators, landscaping the area etc.) are about a cent/kWhr. The killer cost is construction which is all up-front and expensive. It means that once a nuclear power station is up and running it starts paying off the 30 or 40 year financial instrument it took to build it and the owners really want to keep it running 24/7/365 to pay the capital and interest accruing.

Am I the only one who didn't like 1979 the first time, and don't want a replay?

As far as politics goes, yes.

The 50-year-old politicians in office now were 20 in 1979, and now see their world history through the rose-colored glasses of their youth. Without the understanding of what led to problems before, the politicians and policy-makers blunder onward, in blissful ignorance of upcoming crises. Last time these issues came up, everything seemed so simple (as everything usually does to twenty-somethings) that the prerequisite conditions were ignored. Now those conditions have returned,

Lots of good things happened in '79.- Smallpox was eradicated- The Sony Walkman was introduced (am I the only one missing those?)- Sony and Philips presented (prototype) CDs- Voyager I took pictures of Jupiter- Pioneer 11 took pictures of Saturn- Ariane was launched- Usenet started

But I don't want a repeat, because in 1979, we almost ended life on this planet too, when NORAD erroneously detected a large amount of missiles from USSR heading towards the US. An operator had loaded a test tape into the live sy

TMI is ancient technology. Nobody's built one of these things since TMI went online. They built using newer safer designs.

Of course, getting authorisation to shut down, decommission, and dismantle a reactor takes almost as much time, effort, legal fees, and money as building the damned thing in the first place. It's on the order of 4 acts of $DIETY and an act of Congress.

Because a simple mechanical device failed? Wow, that's news. Because the safety measured at the plant functioned exactly as designed? Yup, that's certainly news. Because the residents in the area heard a loud noise? Stop the presses!

Or because when anything happens at a nuclear power plant---including it functioning exactly as designed---the anti-nuclear luddites and other assorted fearmongers leap on the (non-)story in order to push their agenda?

It was a huge deal. A plant with a control system that wouldn't even pass regulations at a fertilizer works showed that you couldn't play fast and loose with nukes just because there were no regs to prevent you doing so, so that meant improvement of some other plants, shutting down some absolute deathtraps of the 50s and 60s, and a move towards better designs.

Due to a combination of nimbyism and practical considerations it's very common to have multiple reactors at one site.

TMI-2 was where the famous accident happens and was shut down permanently due to massive internal radioactive contamination. Afaict TMI-1 has had minor incidents over the years but nothing that would require a permanent shutdown.

There's more than one powerhouse at TMI. Only Unit 2 had the partial meltdown, and was ruined beyond repair. Unit 1 has been operating ever since, as it was powered down for refueling during the events of 1979.

They ARE there for redundancy. For safety reasons, a reactor must not be operated without adequate redundancy. So, one of the redundant pumps failed and the system shut down in an orderly manner. That is necessary since it takes just a wee bit longer to swap in a cold spare pump than it does for a disk in a RAID.

It would be technically possible to run the reactor on 3 pumps but safety would be compromised.

The best way to know a pump will run is to have it running. That's why they keep all 4 running under normal conditions.

That is actually sort of alarming to me since they probably install 4 identical pumps at the same time each with a rated lifetime that is about the same. So when the first fails, the others are surely soon to follow, And that takes us full circle to why if one fails, the system is designed to shut down.

You are right and I sure hope they are running like GP says they are. If you have backup pumps, of course you do not run them like the others. You shouldn't forget about them for twenty years hoping they will just wake up when needed, but running them full-time would be nuts.

This is why, in the nuclear world, they have Quality Assurance paperwork and cradle to grave tracking. They have every test that was ever done to every component of that pump from the time of manufacture until present day. They will be looking at all the data. That "all" includes an awful lot.

Not just in nuclear but in the process industry in general to meet certain risk reduction goals for process safety redundancy is not enough. Redundancy can have failures and the failures require actions to be performed. The way this is typically done is when a piece of equipment has a failure in one of it's areas (say a safety PLC loses a processor card) a countdown timer starts to automated shutdown.

That to me implies that the normal situation is that all 4 pumps must be running, and they are not there for redundancy at all. If not, why have the other 3 pumps there at all?

Using the Raid analogy, it's like having a RAID 5 array. When all the disk drives are working, your data is safe from a single drive failure. You have redundancy and can recreate all your data even if a drive fails. One of your drives then fails and you are no longer redundant, your data remains but you are no longer protected from *another* drive failure. When the data is important enough, you will simply shut down the system until full redundancy is restored.

The fact that it is a nuclear reactor means that it SHOULD have backups, and backups for those backups, and if that should fail, there is a backup for that. Perhaps NASA should run our nuclear power plants.

great it passed the 10 hour test, hows that going to hold when its the only path for a week?

The obvious and straightforward way to handle this is to install redundant pumps, and switch back and forth between them on a schedule which also permits inspection and maintenance. You should have at least two of anything you can reasonably have two of. No, I don't care that it increases the cost. The cost of failure is much higher.

They do have redundancy. The power station is connected by a grid to other power stations.

Well, it's good thing that we cleared that up. I was worrying that redundancy was on-site, not piped in from elsewhere which Fukushima Daiichi proved is a total clusterfuck. I can rest easy knowing that the situation is completely fucked. Wait, what?

The point was that shutting down the reactor is not so bad because they have redundancy at a higher level.For the same reason, if you have a large farm of redundant servers, you do not need redundant PSUs on each.

Fukushima was connected to the grid for "redundancy" too. They also had a large stockpile of batteries on-site and an even larger one off-site. The former was not nearly enough and they couldn't get the latter to site when they needed it, even by helicopter.

What happens when the cutover from one system to the backup system fails? How do you avoid a single point of failure? Yes, you could run both pumps in parallel at half power and devise some means of shutting off a failed pump and running the other at full power. That *still* introduces more complexity and more potential failures.

It's like they say about twin-engine aircraft - if one engine goes, the other has enough power to fly you right to where the crash happens.